Right now the rooms are pseudo-randomly chosen depending on the position. Generally once the couple picks an area they tend to stay near that area for similar poses, like being on the floor, etc. so if you don't like a certain area then choose a different type pose then go back to the original one and it might change.
I'd like to put in something in one of the upcoming updates that will let people choose exactly where to do something, but right now there's no way to explicitly pick.
